Automatic alternator cut out/regen braking

[jpgmtech]

Just a thought, not exactly what is trying to be achieved here but it would help nonetheless. Has anyone tried installing an underdrive pulley? Slow things down, reduce the parasitic drag of the alternator (and water pump, etc.)

[COMP]

Originally Posted by jpgmtech

Just a thought, not exactly what is trying to be achieved here but it would help nonetheless. Has anyone tried installing an underdrive pulley? Slow things down, reduce the parasitic drag of the alternator (and water pump, etc.)

from what i have found out ,thats one of the better mods to do on the 3.0L Dodge i have

[Randy]

I modified my car to not charge via a switch. All the 5th generation Civics have an extra wire on the alternator, which if you ground will reduce the voltage to 12v from 14v. It runs from the ECU to the alternator, which has an internal regulator. The ECU drives it with an open-collector circuit (at least on mine), so grounding it out with a switch doesn't hurt anything.

Does it help the MPG? I have no idea. It dims the lights, and reduces the load due to the lower voltage. It won't kill the battery because it's still above the discharged voltage.

If this wire wasn't there, shutting off the alternator wouldn't be so easy. Alternators self-excite as long as the regulator is in the circuit. Cutting off the field or output via a relay will cause spikes, possibly damaging the regulator. The best cure is a new regulator... a switching regulator would be more efficient than the standard linear type anyway. The other way to go is to add a clamping circuit to absorb the spike. This could be as simple as a diode, but you'd need to test it.

[Gregte]

I just did a little experiment on my 94 GMC Sonoma. I disconnected a small 2 wire plug going to my alternator then started the engine. This caused the battery to not charge as it measured 11.8 volts (low because of having just started the engine). I then plugged the wires back in and the voltage went up to 14.6. I then plugged and unplugged it a few times, engine idling, and detected no discernible change in engine load, i.e. no change in RPM.

Maybe the ECU controls the RPM so well that a small load change is not detectable. Or, maybe the alternator load, particularly if the battery is nearly fully charged already, is negligible.

How much FE gain are you expecting by de-energizing the alternator field, once the battery is fully charged?

[JohnnyGrey]

Maybe the ECU controls the RPM so well that a small load change is not detectable.

Yep. Unplug your IAC valve and retry your experiment. My 2.2L will drop about 40rpm from the headlights, and another 40 if I turn on the seat heater.

[Gregte]

Mine (2.2L) also drops RPM with lights on but disconnecting IAC causes very high RPM, too high to detect a minor load variation I think.

The following is just my personal reasoning, subject to errors but anyway...

I believe, from my measurements, that the alternator on my 2.2L GMC Sonoma is putting 2 to 4 amps into the already charged battery at 14.6v, which of course is wasted as heat. This translates to about 44 watts which is 0.059 horsepower of wasted energy. If you consider that perhaps as much as half of that is lost as inefficiency of the alternator, before it got to the battery (more wasted heat), it then translates to a total loss of 0.059 X 2 = 0.118, or just over one tenth of a horsepower.

My thinking is that it would be better to design a regulator for the alternator that charges the battery at a lower voltage such as anything from 13.4 to 13.8 volts. My understanding from what I have read is that a 12 volt lead acid battery has to have a charge voltage of at least 13.4v or it will never reach a 100% charge which is required for maximum battery longevity as well as optimum battery performance.

Anyway, a lower charging voltage would keep from putting anything but a small trickle charge into the battery once it is charged, therefore no wasted horsepower. The only downside that I can see is that the battery will take longer to reach full charge after cranking the starter to start the motor. Nothing else should ever deplete the battery, other than the starter, except accessories being ON while the motor is OFF. I never have that situation though.

All this is just my thinking. I probably won't try to alter my charge voltage simply for fear of inadvertently screwing something up that will cost money to replace. I live on a very tight budget.

[jpgmtech]

Here is something for further testing: In order to test an alternator's minimum charging voltage point, we would install a 1/4 ohm resistor in the main charging lead to the battery to get the regulator to drop to minimum output. The 1/4 ohm resistor raised the batteries visible impedance to the regulator, causing it to drop to minimum output.

What you are describing does sounds like the minimum output for that alternator.

[diesel_john]

Originally Posted by Randy

I modified my car to not charge via a switch. All the 5th generation Civics have an extra wire on the alternator, which if you ground will reduce the voltage to 12v from 14v. It runs from the ECU to the alternator, which has an internal regulator. The ECU drives it with an open-collector circuit (at least on mine), so grounding it out with a switch doesn't hurt anything.

Does it help the MPG? I have no idea. It dims the lights, and reduces the load due to the lower voltage. It won't kill the battery because it's still above the discharged voltage.

If this wire wasn't there, shutting off the alternator wouldn't be so easy. Alternators self-excite as long as the regulator is in the circuit. Cutting off the field or output via a relay will cause spikes, possibly damaging the regulator. The best cure is a new regulator... a switching regulator would be more efficient than the standard linear type anyway. The other way to go is to add a clamping circuit to absorb the spike. This could be as simple as a diode, but you'd need to test it.

that is what everyone has been looking for and worthy of its own thread perhaps. good info

AXMonster did your alternator type ever respond to your cutoff circuits?

I agree the 3 scenarios for charging would be:
low battery
brake light on
and idle.

[Randy]

Originally Posted by jpgmtech

Here is something for further testing: In order to test an alternator's minimum charging voltage point, we would install a 1/4 ohm resistor in the main charging lead to the battery to get the regulator to drop to minimum output. The 1/4 ohm resistor raised the batteries visible impedance to the regulator, causing it to drop to minimum output.

Nah, that would increase the output, not decrease it. There is a voltage sensor wire on the alternator (most of the time separate from the dash light wire). The main output will go as high as it needs to to maintain voltage on that wire. To decrease the output, you need to increase the voltage on that wire, but it would be unstable if you didn't have it related to the output voltage. Maybe connect a AA battery to it? The current should be quite low.

About the Honda regulator... it might be possible to retrofit it onto another type of alternator. Other than the control wire, it's the same sort of circuit as a normal alternator. And like I mentioned, the control wire is the most basic sort: just ground for 12v, let it go for the normal 14v.

[jpgmtech]

Originally Posted by Randy

Nah, that would increase the output, not decrease it. There is a voltage sensor wire on the alternator (most of the time separate from the dash light wire). The main output will go as high as it needs to to maintain voltage on that wire. To decrease the output, you need to increase the voltage on that wire, but it would be unstable if you didn't have it related to the output voltage. Maybe connect a AA battery to it? The current should be quite low.

Think impedance...